BACTERIA AND DISEASE 409 



breaking down of the tissues. With plenty of rest, good food, 

 fresh air and sunshine, the human body is able to overcome the 

 invasion of these organisms if their presence is detected in time. 

 Disregarded, they will ultimately cause death of the individual 

 attacked. In addition to man, cattle and pigs are particularly 

 susceptible to tuberculosis. Diphtheria is caused by a slightly 

 curved bacillus (fig. 251) which, in addition to producing 

 strangulation of the victim by forming a thick membranous 

 growth in the throat, also produces a powerful toxin which is 

 carried in the blood stream to other parts of the body, where it 

 weakens such vital organs as the heart and kidneys. Tetanus 



A B 



Fig, 252. — Other pathogenic bacteria include (A) pneumonia cocci, and (E) 



cholera spirilla. 



bacilli produce the often fatal "lockjaw." These are common in 

 soil, water, and in the intestinal tract of the horse where they 

 live harmlessly. Introduced into the blood stream and tissues of 

 man, generally by way of nail punctures and similar deep 

 wounds, they multiply rapidly to produce the disease. 



The spherical bacteria or cocci contain a number of the pus 

 forming species common in boils, abscesses, and open wounds. 

 When these organisms gain entrance to the deeper body tissues 

 and blood stream, erysipelas results. Many of the streptococcus 

 forms — chains of cocci — are responsible for infections of the 

 throat and other portions of the respiratory system, as well as 

 some types of dysentery and appendicitis. Other coccus forms — 

 known as diplococci (fig. 252) — occur in pairs and cause 

 pneumonia, meningitis, eye infections, pleurisy, and an often 



